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Homework Help: Initial velocity

  1. Sep 24, 2004 #1
    A ball has an initial velocity of 10 m/s.
    The acceleration of gravity is 9.8 m/s^2.

    What will be it's postion after 2.12794 s if it is throw

    a) down with an initial velocity of 10 m/s? Answer in units of m.

    b) up with an initial velocity of 10 m/s? Answer in units of m.


    I think for b you use:

    y = Vot + 1/2gt^2

    I got 43.47m, but thats wrong.
  2. jcsd
  3. Sep 24, 2004 #2


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    Homework Helper

    I got -1.03, i think your calculations are wrong, and also i forgot if its negative it's pointing down, so it's going down.
    Last edited: Sep 24, 2004
  4. Sep 24, 2004 #3
    use this : y = 10t - 9.8t²/2 and the t is given

    the g-vector points downwards the y axis thus you need to write a minus sign. Watch out when you work with vectors : you have the magnitude of a vector AND the direction of a vector...

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